This invention relates to bearing assemblies which have a wick-type contactor plug for communicating a lubricant reservoir with the bearing surface and more particularly to a method of forming a contactor plug.
It has been found that an effective way to lubricate bearing surfaces, particularly sleeve bearings in electric motors, is to surround the bearing with a reservoir or cavity into which a lubricant-impregnated wicking material is injected. This type of material is well known and is commercially available under the registered trademark "PERMAWICK". Different forms of Permawick material are taught in U.S. Pat. Nos. 2,966,459, 3,214,375 and 3,466,244.
The bearing has an opening in it, referred to as the window, which communicates the shaft with the lubricant-impregnated wicking material. A plug or contactor formed of appropriately-shaped pieces of felt is typically placed in the window to deliver sufficient lubricant by capillary action from the wicking material to the bearing surfaces and to prevent erosion due to fibers in the wicking material being drawn between the bearing and shaft. The use of a contactor to solve this latter problem and to use a contactor for throttling oil from the wicking material to the bearing surface are taught in my U.S. Pat. No. RE 27,998.
Although there are many advantages in using an oil-impregnated wicking material instead of filling the reservoir with oil to lubricate bearing surfaces, one disadvantage is that it has been found that the wicking material does not release all of the lubricating oil contained in it, which necessitates a relatively large reservoir, operates to shorten the effective life of the lubricant and of the bearing surfaces, and results in a significant amount of lubricating oil never reaching the bearing surfaces and being wasted.
One attempt to solve this problem by altering the makeup of the wicking material is taught in U.S. Pat. No. 3,894,956 where a fibrous wicking material formed of foamed polymeric particles is used instead of the materials typically sold under the trademark "PERMAWICK". This material does tend to release more of the impregnated oil over time than the Permawick materials, but problems have developed because the oil tends to be released from the particles at a rate which is too high and which contributes to oil leaking from the bearing and prevents the wicking material from reabsorbing the oil as fast as it should.
Another problem with the bearing assemblies of the type described above has been found to stem from the type of contactor which is used. In the past, these contactors have typically been formed by cutting or stamping appropriately shaped pieces from a relatively large sheet of commercially available felt. Care must be taken in cutting the contactor and assemblying it in the window because contactors with different flow characteristics result if all the contactors cut from the same sheet are not positioned so that their fibers are oriented in the same direction. Furthermore, it has also been found that flow characteristics oftentimes differ when contactors are cut from different sheets even though the felt is graded the same, which makes it difficult to predict relative performance levels. Another problem is that the surface of the felt which contacts the shaft tends to become glazed due to deterioration of the wool fibers which make up the felt. The glazing plugs the openings in the contactor and lowers the ability of the contactor to transfer oil from the wicking material to the bearing surface, which increases frictional heat and contributes to a shorter bearing life.